Our aims are: to provide detailed descriptions of the molecular geometries of nucleic acids and polynucleotides using X-ray diffraction analysis of oriented fibers; to collate the information obtained so that it may be of use in fabricating models of the structurally more complex polynucleotide chains that occur in transfer RNA, ribosomes and viruses; to formulate and, if possible, test the dependence of biological function on molecular geometry (e.g. interferon induction); to develop models for the interaction of chemotherapeutic agents and antimetabolites that bind directly to nucleic acids or (like strange nucleotides) become part of their chemical constitution.